"The Second Amendment ... is not, was never and should not be designed to arm foreign criminal groups," Mexican Ambassador Eduardo Medina Mora told reporters last week.

His comments were just the latest in years of criticism of U.S. gun policies by Mexican officials, who blame weapons trafficking from the United States and the 2004 expiration of the U.S. assault weapons ban for fueling brutal drug violence south of the border.

Now, the issues many Mexicans felt Washington had neglected are in the spotlight.

NRA ad criticizes President Obama

And with indignation over guns growing in the United States, reforms that Mexico has long awaited may come through, Medina said.

Mexico will keep pushing for better U.S. gun regulation, he said, noting that an assault weapons ban is one constitutional option.

The end of the ban in 2004 impacted Mexico, he said.

"There is certainly a statistical correlation between the end of this measure and the increase in the firepower of foreign criminal groups, particular those that operate out of our country," he said.

On Monday, prominent Mexican peace activists renewed their call for the United States to stop weapons trafficking across the border, saying that the Connecticut shooting made the need for action all the more clear.

"We wish to convey our deepest condolences over the repeated slaughter of innocents in your country. As parents and grandparents, the killing of innocent children in Newtown (Connecticut) has moved us deeply," Mexico's Movement for Peace with Justice and Dignity said in a petition delivered to the U.S. Embassy in Mexico City.

"Consequently," the petition continued, "we are disconcerted and offended by the indifference of the United States toward the massacres that daily plunge Mexico into mourning."

Nearly 70% of the 99,000 weapons seized in Mexico from 2007 to 2011 came from the United States, the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives said last year.

That issue surged to the fore in Washington last year, amid a U.S. congressional inquiry into "Operation Fast and Furious," an operation run by U.S. federal agents. Authorities have said the operation was intended to track the flow of illegally purchased American guns to the Mexican cartels, but in practice, ATF agents allowed so-called straw buyers to take weapons across the border without being intercepted.

In Mexico's capital, authorities have started an exchange program to try to stem gun violence.

In one Mexico City neighborhood last month, residents handed in hundreds of guns in exchange for money vouchers. Handguns, high-caliber weapons and even a hand grenade were among the weapons authorities collected. As part of the program, children also swapped toy guns for bicycles, electronic devices and toys.

Americans on the other side of the border were the intended audience for the English-language sign, then-President Felipe Calderon said at the time, saying an increase in violence in Mexico was directly connected with the 2004 expiration of the U.S. assault weapons ban.

"The criminals have become more and more vicious in their eagerness to spark fear and anxiety in society," he said. "One of the main factors that allow criminals to strengthen themselves is the unlimited access to high-powered weapons, which are sold freely, and also indiscriminately, in the United States of America."